Fact Sheet ST-279
November 1993
Gleditsia triacanthos var. inermis
Thornless Honeylocust1
Edward F. Gilman and Dennis G. Watson2
INTRODUCTION
Honeylocust grows quickly to 70 feet or more
with an oval or rounded canopy (Fig. 1). The species
has undesirable thorns on the trunk and main branches
and large seed pods so it is best to plant selections of
the variety inermis which are both thornless and some
nearly seedless. Some leaves on the tree are
bipinnately compound, others are pinnately compound.
The seed pods look rather unsightly hanging on the
tree into the fall and make quite a mess as they litter
the ground below the canopy. The tree is strongwooded and casts light shade. Lawns grow fairly well
beneath the tree and there is little to rake up in the fall
since the tiny leaflets filter in between the blades of
grass or are washed away in the rain. Honeylocust has
a yellow or golden fall color in the northern part of its
range. Trees often defoliate early in the south and are
bare by October.
GENERAL INFORMATION
Scientific name: Gleditsia triacanthos var. inermis
Pronunciation: gleh-DIT-see-uh try-uh-KANTH-oase
variety ih-NER-miss
Common name(s): Thornless Honeylocust
Family: Leguminosae
USDA hardiness zones: 3 through 8A (Fig. 2)
Origin: native to North America
Uses: large parking lot islands (> 200 square feet in
size); wide tree lawns (>6 feet wide); recommended
for buffer strips around parking lots or for median strip
plantings in the highway; reclamation plant; shade
tree; specimen; sidewalk cutout (tree pit); residential
street tree; tree has been successfully grown in urban
Figure 1. Young Thornless Honeylocust.
areas where air pollution, poor drainage, compacted
soil, and/or drought are common
Availability: generally available in many areas within
its hardiness range
DESCRIPTION
Height: 50 to 75 feet
Spread: 35 to 50 feet
Crown uniformity: irregular outline or silhouette
1.
This document is adapted from Fact Sheet ST-279, a series of the Environmental Horticulture Department, Florida Cooperative Extension Service,
Institute of Food and Agricultural Sciences, University of Florida. Publication date: November 1993.
2.
Edward F. Gilman, associate professor, Environmental Horticulture Department; Dennis G. Watson, associate professor, Agricultural Engineering
Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville FL 32611.
Gleditsia triacanthos var. inermis -- Thornless Honeylocust
Page 2
Figure 2. Shaded area represents potential planting range.
Crown shape: oval; round
Crown density: open
Growth rate: fast
Texture: fine
Foliage
Leaf arrangement: alternate (Fig. 3)
Leaf type: bipinnately compound; odd pinnately
compound
Leaflet margin: crenate
Leaflet shape: lanceolate; oblong
Leaflet venation: pinnate
Leaf type and persistence: deciduous
Leaflet blade length: less than 2 inches
Leaf color: green
Fall color: copper; yellow
Fall characteristic: showy
Flower
Fruit
Fruit
Fruit
Fruit
Fruit
Fruit
shape: elongated; pod
length: 12 inches or more; 6 to 12 inches
covering: dry or hard
color: brown; purple
characteristics: does not attract wildlife; fruit,
twigs, or foliage cause significant litter; persistent on
the tree; showy
Trunk and Branches
Trunk/bark/branches: grow mostly upright and will
not droop; showy trunk; should be grown with a single
leader; no thorns
Pruning requirement: requires pruning to develop
strong structure
Breakage: resistant
Current year twig color: brown
Current year twig thickness: thick
Flower color: yellow
Flower characteristics: pleasant fragrance;
Culture
inconspicuous and not showy; spring flowering
Light requirement: tree grows in part shade/part sun;
tree grows in full sun
Gleditsia triacanthos var. inermis -- Thornless Honeylocust
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Other
Roots: surface roots can lift sidewalks or interfere
with mowing
Winter interest: tree has winter interest due to
unusual form, nice persistent fruits, showy winter
trunk, or winter flowers
Outstanding tree: not particularly outstanding
Invasive potential: little, if any, potential at this time
Ozone sensitivity: sensitive or moderately tolerant
Verticillium wilt susceptibility: not known to be
susceptible
Pest resistance: long-term health usually not
affected by pests
USE AND MANAGEMENT
Some cultivars, especially ‘Skyline’ grow a central
leader and would require little pruning but others grow
many upright codominant trunks. These trees will
need to be trained when they are young by two or
three prunings spaced several years apart. Strive to
develop one central trunk with upright spreading
branches spaced several feet apart along the trunk.
Purchase good quality trees with one leader in order to
reduce the pruning requirement.
The tree has no particular soil preferences and is
useful in dry or alkaline areas, although its native
habitat is along stream banks. It tolerates compacted,
poorly aerated soil and flooding for a period of time
and does well in confined soil spaces. Honeylocust
adapts well as a city street tree and is tolerant to small
planting pits in concrete. It is susceptible to breakage
in ice storms.
Unfortunately, it has been overplanted in some
areas and insect problems are beginning to catch up
with Honeylocust, including the cultivars.
Recommend planting in moderation to avoid
catastrophe if insects or diseases invade. It might be
best to plant Pistacia, Zelkova, Taxodium, Quercus or
some other proven urban tough tree in place of
Honeylocust to avoid potential insect, disease and
early defoliation problems in the South.
Figure 3. Foliage of Thornless Honeylocust.
Soil tolerances: clay; loam; sand; acidic;
occasionally wet; alkaline; well-drained
Drought tolerance: high
Aerosol salt tolerance: high
Soil salt tolerance: good
Most garden centers will have at least one cultivar
of Honeylocust in stock. Some of the cultivars may
develop thorns and/or seed pods when they get older
and they may be best suited for areas north of USDA
hardiness zone 8b. The cultivars are: ‘Cottage Green’
- semi upright, seedless, thornless; ‘Imperial’ - uprightspreading, seedless, and thornless until 10 to 15-years-
Gleditsia triacanthos var. inermis -- Thornless Honeylocust
old when some seeds do develop; ‘Majestic’ - upright,
seedless, thornless; ‘Maxwell’ - upright, seedless,
thornless; ‘Moraine’ - spreading, usually seedless,
thornless; ‘Rubylace’ - new reddish foliage, seedless,
thornless, color not outstanding, may need staking
when young; ‘Shademaster’ - upright, spreading,
usually seedless and thornless until 10 to 15-years-old
when some seeds do develop - perhaps the best
cultivar; ‘Skyline’ - pyramidal with a dominant central
leader, generally seedless, thornless; ‘Sunburst’ - new
yellow foliage, seedless, thornless, favored by plant
bugs and leafhoppers.
Pests
Mimosa webworm has become a serious pest on
Honeylocust in some communities.
Boring insects may be largely prevented by
keeping trees healthy with regular fertilization. They
usually attack trees under stress from other problems.
The combination of plant bug and leafhopper
feeding causes the leaves to drop. Plant bugs may be
more common on the yellow leaved cultivar ‘Sunburst’
than on green leaved types. Both insects are green so
they will be hard to detect.
Pod gall midge causes unusual reddish galls at the
tips of the branches. Leaflets become pod-like. The
galls appear in late spring and may be most common
on thornless, seedless cultivars. These have become
quite a problem in many areas. Control is difficult.
Spider mites cause an autumn-like yellowing of
the leaves. Diagnosis of this problem is difficult due
to the small size of the insect and leaflets. Look for
the mites and their webbing near the midrib at the base
of the leaflets.
Leafminers and bagworm can also be a problem.
Aphid infestations can be troublesome.
Diseases
Canker causing fungi or bacteria attack branches
and trunks causing dieback of parts or the entire tree.
Keep the trees healthy and avoid unnecessary
wounding. Infected areas have discolored bark,
peeling bark, discolored sapwood, or a crack between
the diseased and healthy bark. The ronectria canker is
especially damaging.
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There is a leaf spot may be a problem. Rake up
and dispose of infected leaves.
Powdery mildew may cause a white coating on the
leaves but is seldom serious.